1. Field of the Invention
The alarm concerns an alarm sensor with a radar detector for activating a target tracking tracker upon the approach of a target which is to be potentially combatted; in particular, a missile which is approaching a land vehicle or marine craft and which is to be defended against.
2. Discussion of the Prior Art
Alarm or wake-up sensors of that kind are known for example from DE 35 15 496 A1 or DE 38 37 483 A1 for activating and directing stationary defence means (in mine form) against flying target objects approaching at relatively low height such as in particular battle helicopters, with passive or active alarm sensor detectors responding to their (sound) radiation or (rotor) modulation.
The present invention however concerns in particular a wake-up or alarm sensor for switching a target tracking apparatus, a so-called tracker, onto an attacking missile which is to be repelled. The target tracking apparatus may be in accordance with DE 36 08 108 C1 a navigational computer for detecting and extrapolating the current trajectory of the missile to be repelled; or in accordance with DE 44 30 830 A1 or DE 44 26 014 A1 it may be a reflection location tracker which with its spatial orientation follows the relative position of the missile after the approach flight thereof has once been detected.
As a missile to be repelled does not have the pronounced signature of a battle helicopter to be defended against and approaches the endangered object at a substantially faster speed, an alarm sensor which operates with passive detectors cannot be readily used with a high prospect of success in missile defence situations. An active alarm sensor which is therefore based on a reflection location function on the other hand suffers from the disadvantage of a high probability of betraying itself, which exposes it to attack by anti-radar missiles which are optimised in relation thereto.
The danger of self-betrayal however is avoided in the case of a passive bistatic radar system, as is described in U.S. Pat. No. 5 424 744: in that case the alarm procedure is initiated by virtue of the fact that the instantaneous reception connection from a potentially threatened object such as in particular an aircraft to a constantly transmitting satellite, in particular a navigational satellite which is low above the horizon, is at least temporarily significantly disturbed because a missile approaching the object crosses that radio communication direction and thereby causes reflection or shadowing phenomena. Although the object to be protected, for position determining purposes, continuously receives at least four satellites in different positions, among those there are however always also some which at a given moment are not in the desirable position of being near to the horizon or whose relative position in relation to the endangered object, as regards a significant disturbance in the radio communication, is disadvantageous in regard to the direction of approach of the attacking missile, in consideration of the large distance to the object. That results in particular in observation gaps and thus situations involving a threat from changing directions which are not predictable, if an attacking missile is to be detected at the greatest possible distance from the object to be protected, in order to be able to make the defences ready for operation in good time.